1. Field of the Invention
This invention relates to a nailable steel flooring for freight handling vehicles, and more particularly to nailable steel floor planking members having an improved anti-skid load bearing surface and to a method of manufacturing such planking members.
2. Description of the Prior Art
Freight handling vehicles such as trucks and rail cars, hereinafter generally referred to as cars or rail cars, are known in which the load supporting floor is constructed of transversly extending steel planking members supported on longitudinally extending beams or girders. The planking members have conventionally been of a generally channel shaped construction with the central web of the channel forming the load bearing surface and the side flanges extending downwardly and being supported on the girders. The side flanges are generally of complex shape and may include inwardly directed terminal portions which engage the girders to support the floor structure. The downwardly extending portions of the side flanges are normally of compound-curve configuration and include spacer members for engaging the side flanges of adjacent planking members to provide a nailing groove for securing articles to the floors to prevent shifting during hauling. The cooperating compound-curved side flanges of adjacent planking members are of complementary nature to provide a substantially uniform spacing in the nailing grooves. It is also known to reinforce the channel members by a structural member extending beneath and welded to the bottom surface of the central web of the channel.
As is well known, the prior art nailable steel floorings have generally had relatively low friction load support surfaces, which surfaces tend to become more slippery with use as a result of the polishing effect of articles being moved over the surface during normal use. This slippery condition of the floors is accentuated by foreign matter such as oils, water and other liquids or fine solids such as grains, sand, granular or pelletized chemicals or the like which are frequently spilled on the floor. This slippery condition not only increases the loads placed on the nails driven into the nailing grooves to anchor the individual articles for shipping, but also presents a substantial hazard to personnel loading and unloading the cars and can make it difficult to maneuver material handling equipment such as forklift trucks or the like commonly used in loading and unloading cars.
Attempts have been made to provide a anti-skid surface on nailable steel flooring planks, but the prior art attempts have not been entirely satisfactory and are not widely used. One such prior art system is shown in U.S. Pat. No. 2,670,060 which discloses the concept of providing a anti-skid surface on a nailable steel flooring plank by forming a series of transversly extending channel-like depressions in the top of the flooring planks to structurally reinforce the web of the channel, and then filling the depressions with a resilient anti-skid material. While this material is effective in providing a less slippery surface for load handling equipment and personnel, it has limited effect on heavy, rigid articles which are supported primarily by the metal surface as on metal bases, wooden pallets, skids or the like.
It is also known to apply a anti-skid metal sheathing to the load bearing surface of non-metal floors, for example wooden floors, one such system being shown in U.S. Pat. No. 3,365,221. The metal sheathing disclosed in this patent has a number of circular openings formed by a punching operation which results in the periphery of the openings having sharp, upturned edges which provide the anti-skid feature of the surface. Articles may be secured to the wooden floor beneath the sheathing by nails driven through the circular openings. The sheathing is secured to the wooden floors by spikes struck from the metal plate used to form the sheathing.
Anti-skid surfaces are also commonly provided on metal plate members employed as walkways, stair-treads, catwalks, ladder rungs, balconies, and the like. Such known anti-skid surfaces include raised portions formed in a continuous pattern on one surface of metal plate, open gratings such as expanded metal, and patterns formed by rupturing and/or deforming segments of an original smooth, flat metal plate. A anti-skid panel formed by the latter method is disclosed in U.S. Pat. No. 3,093,216 in which relatively thin gauge flat metal plate is initially provided with a series of parallel strengthening ribs, with rows of conical, sharp edges openings formed between the ribs. The ribs are of a height to enable trucks to roll therealong without being pumped by the conical, perforated anti-skid bumps, or openings. After the ribs and perforations are formed in the respective plates, the edges are turned under to form a channel shaped pannel.
The relatively heavy gauge metal required to provide the strength and damage resistance required in a railway car floor, and the high speed precision forming techniques required for commercial production of nailable steel floor planking members, make it impractical to manufacture such planking members from sheet stock having anti-skid elements preformed on its surface. Such commercial production techniques require the main channel element of the planking members to be continuously roll formed from strip stock supplied to the forming apparatus in large coils. The strip is unwound and passed through straightening rolls before being passed to and through a series of pairs of forming rolls to be progressively roll formed to the channel configuration. Accurate control of the forming operation is necessary in order to provide the necessary close tolerances on the nailing groove provided between adjacent planking members in a flooring assembly. This groove must be of sufficient width to permit the driving of nails into the groove with the nail following the compound-curve configuration of the channel flanges and with the spacing of the flanges being such as to provide the necessary degree of frictional resistance to withdraw the nail to enable heavy freight articles to be firmly secured in position on the floor. The rolling operation necessarily requires firm contact between the forming rolls and the flat surface of the strip stock being rolled into the planking channel.